1. Field of the Invention
The present invention relates to a thin-film magnetic head including a toroidal coil layer, for example, used for a floating-type thin-film magnetic head unit. More particularly, the invention relates to a thin-film magnetic head including a toroidal coil layer in which the heat capacity is increased in a region extending in the height direction at the back of the toroidal coil layer and in which excellent heat dissipation ability is exhibited.
2. Description of the Related Art
Recently, thin-film magnetic write heads (inductive heads) provided with core layers and coil layers have been miniaturized as recording densities have been increased. Consequently, coil layers must be formed by winding in very small spaces.
Instead of thin-film magnetic heads having a spiral coil structure which uses a space between a lower core layer and an upper core layer and in which a coil layer is spirally wound around a connecting section which connects the lower core layer and the upper core layer to each other, thin-film magnetic heads having a toroidal coil structure in which a coil layer is toroidally wound around a core layer are thought to become mainstream inductive heads.
In the miniaturized inductive heads using such a toroidal coil layer, the following problem has particularly become obvious. That is, in the inductive head with the toroidal structure, since the coil layer is integrated in the front region in the height direction, Joule heat generated by a recording current flowing through the coil layer and heat due to an eddy current generated in the core are not easily dissipated efficiently from the inductive head. As a result, the temperature inside the inductive head is remarkably increased.
If the temperature inside the inductive head is increased, a so-called “pole tip protrusion (PTP)” phenomenon occurs, i.e., due to the difference in the coefficient of thermal expansion between the coil layer or the core layer composed of metallic materials and the insulating material surrounding them, the inductive head section is likely to protrude from the surface facing a recording medium compared to the other section.
In particular, in the thin-film magnetic head in which a high recording density is enabled, because of the high frequency of the recording current applied to the toroidal coil, the temperature inside the inductive head is rapidly increased, and protrusion from the surface facing the recording medium increases. If the inductive head protrudes from the surface facing the recording medium, the inductive head is more likely to collide with the recording medium, thereby damaging the recording medium or being damaged by the recording medium.
Thin-film magnetic heads in which heat generated in the inductive heads can be dissipated and the PTP phenomenon can be inhibited are disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2001-093113 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 2001-126216 (Patent Document 2), and Japanese Unexamined Patent Application Publication No. 7-282419 (Patent Document 3).
The thin-film magnetic head according to Patent Document 1 has the toroidal structure as that described above. In this thin-film magnetic head, a lower core layer extends in the height direction at the back of a back gap layer disposed on the lower core layer. The lower core layer in the region at the back of the back gap layer is thought to function as a heat-dissipating member for dissipating heat generated in the coil layer and the core layer.
However, in the thin-film magnetic head according to Patent Document 1, the back gap layer has a small length in the height direction and has a small volume. Generally, in the inductive head, aside from heat generated in the coil layer and the core layer, heat is also generated from the back gap layer due to an eddy current occurring in the back gap layer. In the thin-film magnetic head according to Patent Document 1, since the volume of the back gap layer is small, the heat capacity of the back gap layer is small, and the heat dissipation effect is small. An insulating layer is disposed above the lower core layer at the back of the back gap layer, and thereby the ability to effectively dissipate heat transmitted to the back region of the lower core layer is small.
In the thin-film magnetic head according to Patent Document 2, as shown in FIG. 8, etc., of Patent Document 2, a back gap layer extends in the height direction. The back gap layer is thought to function as a heat-dissipating member for dissipating heat generated in the coil layer and the core layer.
However, since the thin-film magnetic head according to Patent Document 2 has a spiral coil structure in which the coil layer is spirally wound around the back gap layer, the coil layer is also disposed at the back of the back gap layer and at the sides of the back gap layer. Therefore, there are limitations in forming the back gap layer with a large area extending longitudinally in the height direction or extending laterally in the track width direction, and thereby there are limitations in allowing the back gap layer to effectively function as the heat-dissipating member.
In the thin-film magnetic head according to Patent Document 3, a connecting section disposed at the back of an upper core layer and a lower core layer for connecting both core layers is thought to function as a heat-dissipating member for dissipating heat generated in the coil layer and the core layers.
However, since the thin-film magnetic head according to Patent Document 3 also has the spiral coil structure as in the thin-film magnetic head according to Patent Document 2, the coil layer is spirally wound around the connecting section.
Therefore, there are also limitations in forming the connecting section with a large area, and thereby there are limitations in allowing the connecting section to effectively function as the heat-dissipating member. In the thin-film magnetic head according to Patent Document 3, first of all, since the connecting section is composed of the upper core layer and the lower core layer, an increase in the size of the connecting section itself is limited, and thereby there are limitations in allowing the connecting section to function as the heat-dissipating member.